The skull indicates that the child who lived about 530,000 years ago would have been severely handicapped — and yet survived at least five years and possibly several years longer. That suggests the parents or community provided the child with care, despite his or her obvious deformities.

"Her/his pathological condition was not an impediment to receiv[ing] the same attention as any other Middle Pleistocene Homo child," the the team of Spanish researchers write in the Proceedings of the National Academy of Sciences.

The way that humans take care of the sick and infirm within their communities is considered a unique trait. Researchers call it conspecific care, but most laypeople would probably call it compassion. Other primates don’t display similar behavior, so we know humans evolved the ability at some point, even if scientists can’t quite pinpoint when. The work could mean that humans as far back as half a million years ago had differentiated from our primate ancestors.

By reconstructing the skull from a bunch of pieces, the team was able to determine that the child likely suffered from craniosynostosis a debilitating genetic disorder in which some pieces of the skull fuse too quickly, causing pressure to build in the brain. While they couldn’t tell the exact level of mental retardation likely to result from the malformation, it would have been considerable, requiring large amounts of extra care from the prehistorical human community.

But Stanford University anthropologist David DeGusta points out that several species of primates have been observed to care for abnormal young. That’s a different type of behavior, he said, from adults caring for other adults.

"The survival of an infant with significant pathology has been observed in a range of primate species," he wrote in an e-mail to Wired.com. "Extra caregiving behavior towards such infants has been documented in wild monkeys. Caring for infants is, after all, a key adaptation of mammals in general."

Several studies have shown that young, deformed primates were cared for by their mothers anyway, he said. For example, a 1973 paper reported that blind macaque infants were cared for by their mothers for up to a year.

"Defective infants are not killed by the group even in crowded conditions; compensatory care is given during the first year, primarily by the mother and to a certain extent by other animals in the group," wrote the paper’s author, Gershon Berkson, who was a physical anthropologist at the University of Illinois-Chicago.

Care, in this case, would have extended beyond infancy, but DeGusta argued that 5-year-olds were still largely dependent on their parents.

"This individual probably depended more so on parents, but the other 5-year-olds were still at the mercy of adults," DeGusta said.

DeGusta also had a more methodological objection to many studies that attempt to infer behavior from skeletal remains.

"We just know that this individual survived. We don’t know the circumstances," he said. "I’m not saying their interpretation is unreasonable, but we’re trying to do science, so we have to ask, ‘How would we know that we were wrong?’"

DeGusta argues that it’s hard to judge caring behavior from a very limited fossil record, particularly when the primate record seems to indicate that great apes can survive a variety of horrific injuries.

"My contribution, such as it was, was to say, what’s the baseline here? What kind of illnesses and injuries can nonhuman primates survive?" he said. "We’d love to know things like, when does caretaking begin? … So far, though, those behaviors don’t leave clear, unambiguous records."